accounts: Refresh completion model when scanning from qr code

In that case, we add the provider automatically for the user, not refreshing
the completion model means that the user will get a new dialog form to
create the provider a second time with less accurate information than
what exists in the otp uri.

Fixes #422
Fixes #408

src/widgets/accounts/add.rs

@@ -258,6 +258,8 @@ impl AccountAddDialog {
             )
             .ok();
 
+        imp.provider_completion
+            .set_model(Some(&self.model().completion_model()));
         self.set_provider(provider);
     }